# Why the Sam Hill don't I have DC in my house? **URL:** \ **Category:** Factual Questions\ **Created:** [June 24, 2009, 11:59pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891 "2009-06-24T23:59:43Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![BrandonR](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@BrandonR](https://boards.straightdope.com/u/BrandonR)\ **Post date:** [July 2, 2009, 11:30pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/81 "2009-07-02T23:30:19Z")
> [@Musicat](#): > > Maybe that worked because _it was a good idea,_ with obvious advantages, had manufacturers behind it, and the tech public was clamoring for a solution to device interconnection problems, and they really wanted it. > > Besides, nobody _modified_ their computers to wait for USB. The new versions just incorporated it, for the reasons given above. Right on. Comparing USB & computers to a new electrical system for houses is a bad comparison. Nobody expects to have a computer more than a few years, and it’s often cheaper/easier/makes more sense to buy a new computer than to continuously upgrade components from an old one. The same is definitely not true for a house. USB succeeded because people are constantly throwing old computers away and buying new ones once they become obsolete. Houses have a much lower turnover. ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [July 3, 2009, 12:17am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/82 "2009-07-03T00:17:32Z")
> [@](#): > > When using a combined data/power connector, HorseloverFat brought up an excellent and overlooked point, regarding security. Any USB-like standard would have to address it, such as by having different shaped connectors (a power connector would be visibly missing the data pins). Ah, but you cant. The USB protocol does a digital handshake and asks power. If you remove the data pins then you cant ask for anything, so you get the default output of 100mw. You wont be getting that 500mw without data pins. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 12:34am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/83 "2009-07-03T00:34:24Z")
Anyone besides **sailor** have something they’d like to contribute to the discussion? ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 12:36am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/84 "2009-07-03T00:36:17Z")
> [@HorseloverFat](#): > > Ah, but you cant. The USB protocol does a digital handshake and asks power. If you remove the data pins then you cant ask for anything, so you get the default output of 100mw. You wont be getting that 500mw without data pins. Right. So you would implement a simple protocol through the power pins, separate from the full-fledged protocol going through the data pins. Slightly less elegant, yes, but carrying a 100kbps protocol over an otherwise DC link is trivial. > [@BrandonR](#): > > Right on. Comparing USB & computers to a new electrical system for houses is a bad comparison. Nobody expects to have a computer more than a few years, and it’s often cheaper/easier/makes more sense to buy a new computer than to continuously upgrade components from an old one. The same is definitely not true for a house. USB succeeded because people are constantly throwing old computers away and buying new ones once they become obsolete. Houses have a much lower turnover. USB has been around for ~12 years, and looks like it’ll be around for another 20. Besides, switching out a wallplate every few decades is easy, especially if it doesn’t contain dangerous voltages. ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [July 3, 2009, 12:46am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/85 "2009-07-03T00:46:09Z")
> [@](#): > > Right. So you would implement a simple protocol through the power pins, separate from the full-fledged protocol going through the data pins. Slightly less elegant, yes, but carrying a 100kbps protocol over an otherwise DC link is trivial. ’ Ok, I engineered it. Its in my pocket. I sell it to the chinese government, but they go ahead and put in the regular chipset in the airports so they can steal data. See? Its a trust issue. USB devices lack security controls for the most part. Again, the USB protocol is horrible for public use as a charging protocol. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 12:51am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/86 "2009-07-03T00:51:45Z")
No, ok, I’ll address one thing sailor said (though not for his benefit, since he surely won’t read this or think about it seriously). > [@sailor](#): > > Ok, let’s do some math. What size wires do you need to feed 200 W at 12V over a distance of 100’ with 5% voltage drop max? > > The answer is 10 times more section than at 120 V. Do you know what the going price of copper is? > … > Let us stop with the handwaving and general assertions and put some numbers on this. 16 amps is in the league of what a 120VAC circuit is rated for. So basically… you’d use the same size wire. A room-wide circuit rated for 150W would be a good baseline: more than enough for all the small devices that are the majority of the wallwart users, and a bit of power for a few bigger things, such as a laptop. But what is interesting, is that smart technologies could cut down on the huge safety margins built into modern electrical codes. For example, you could monitor the voltage drops and detect overheats (since high temperature raises the resistivity of the wire, or use a special thermocouple wire). Current codes call for wires of far greater thickness than necessary in an attempt to avoid, under almost all circumstances, runaway reactions that heat wires until they burst into flames. Active protection could let wire thickness be drastically reduced. Another possibility is to distribute medium-voltage DC centrally (ie, 48V), and then use small, compact DC-DC converters to output 12V at the outlet. The outlet might output both 12V (max of 2A/25W) and 48V (max of 16A/800W, shared by all devices on the circuit). Moreover, it’s even possible for the same physical jacks to output either 12V or 48V, using a similar voltage negotiation as FireWire. All these “smart” technologies sound gee-wiz but would be very inexpensive, to which the USB and FireWire standards are testament. (Anything that is build into a motherboard costs peanuts.) A single integrated circuit would take care of all the negotation/sensing/intelligence roles, and be mass-produced for pennies. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 12:54am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/87 "2009-07-03T00:54:51Z")
> [@HorseloverFat](#): > > I sell it to the chinese government, but they go ahead and put in the regular chipset in the airports so they can steal data. See? Its a trust issue. USB devices lack security controls for the most part. Again, the USB protocol is horrible for public use as a charging protocol. I don’t understand. The low-speed power-pin protocol couldn’t be used to steal your data. Your cellphone just would have never been designed to upload data along the power-pins. (Unless there’s some big conspiracy to do design it for this anyway.) You made an excellent point regarding USB, but I’m not sure what you’re arguing now… ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [July 3, 2009, 12:59am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/88 "2009-07-03T00:59:05Z")
If we want 48v why isnt anyone singing the praises of power over ethernet for a defacto DC standard. We already have the specs and products in the market. You home can always use cat5 for phone, iptv, internet, etc. You plug your device into a powered hub and off you go. You can get up to 30W of power. Unlike usb, most ethernet devices have some kind of security built in (firewalls, access control,) and its a data line too so you can do all the smart home/smart energy stuff you want to. I think its a great idea, but no demand for it. Personally, im much more interested in [contact and wireless charging like the palm pre does](http://www.engadget.com/2009/01/08/palm-pres-wireless-charger/). Id love a long pad of this stuff on my kitchen counter where I can toss my phone, laptop, camera,mp3 player, etc and have them negotiate a proper level of power and charge without me messing with cables ever again. Toss in wifi and they can do data while charging. I could see myself spending a little coin for that. DC outlets? Not so much. USB everywhere? No thanks. These are yesterday’s problems and yesterday’s technologies. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 3, 2009, 1:10am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/89 "2009-07-03T01:10:36Z")
> [@sailor](#): > > Ok, let’s do some math. What size wires do you need to feed 200 W at 12V over a distance of 100’ with 5% voltage drop max? > > The answer is 10 times more section than at 120 V. Actually it’s 100 times, if we assume the 120V device and the 12V device can both accept a 5% voltage drop. (120V +/- 5% means 120+/-6 V. 12V +/-5% is 12+/-0.6 V. The 12V circuit has 10 times higher current, _and_ must have 1/10 the voltage drop to maintain 5% accuracy, so wire resistance must be a factor of 100 smaller.) ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 3, 2009, 1:19am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/90 "2009-07-03T01:19:19Z")
> [@Alex\_Dubinsky](#): > > No, ok, I’ll address one thing sailor said (though not for his benefit, since he surely won’t read this or think about it seriously). > > 16 amps is in the league of what a 120VAC circuit is rated for. So basically… you’d use the same size wire. > > A room-wide circuit rated for 150W would be a good baseline: more than enough for all the small devices that are the majority of the wallwart users, and a bit of power for a few bigger things, such as a laptop. Same current, same wire, same voltage drop: 1/10th the power, 10 times the voltage drop as regards voltage. 6V drop in 120 V is 5% and acceptable. 6V drop in 12 is no longer 12 V. And this for 1/10th the power which can be transmitted using 120 V. And 50% lost in the wire. I do not think you have thought this through have you? Again, give us some concrete numbers of what you propose. > [@Alex\_Dubinsky](#): > > But what is interesting, is that smart technologies could cut down on the huge safety margins built into modern electrical codes. For example, you could monitor the voltage drops and detect overheats (since high temperature raises the resistivity of the wire, or use a special thermocouple wire). Current codes call for wires of far greater thickness than necessary in an attempt to avoid, under almost all circumstances, runaway reactions that heat wires until they burst into flames. Active protection could let wire thickness be drastically reduced. > > Another possibility is to distribute medium-voltage DC centrally (ie, 48V), and then use small, compact DC-DC converters to output 12V at the outlet. The outlet might output both 12V (max of 2A/25W) and 48V (max of 16A/800W, shared by all devices on the circuit). Moreover, it’s even possible for the same physical jacks to output either 12V or 48V, using a similar voltage negotiation as FireWire. > > All these “smart” technologies sound gee-wiz but would be very inexpensive, to which the USB and FireWire standards are testament. (Anything that is build into a motherboard costs peanuts.) A single integrated circuit would take care of all the negotation/sensing/intelligence roles, and be mass-produced for pennies. Simplifying things, eh? Having seen all the bellyaching that transpired about transitioning to digital TV I would like to see how this would go through. Yes, you no longer need the wall-wart. You only need an intelligent central power system connected to the peripheral power units , all buried in the walls and then intelligent devices which can communicate with the central power unit. And for the devices you already have? Oh, we will sell you an adapter box which costs ten times more than the wallwart and the device together. Suuuuuuure. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 3, 2009, 1:20am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/91 "2009-07-03T01:20:43Z")
> [@scr4](#): > > Actually it’s 100 times, if we assume the 120V device and the 12V device can both accept a 5% voltage drop. > > (120V +/- 5% means 120+/-6 V. 12V +/-5% is 12+/-0.6 V. The 12V circuit has 10 times higher current, _and_ must have 1/10 the voltage drop to maintain 5% accuracy, so wire resistance must be a factor of 100 smaller.) You are right, of course. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 3, 2009, 1:25am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/92 "2009-07-03T01:25:32Z")
> [@HorseloverFat](#): > > If we want 48v why isnt anyone singing the praises of power over ethernet for a defacto DC standard. We already have the specs and products in the market. You home can always use cat5 for phone, iptv, internet, etc. You plug your device into a powered hub and off you go. You can get up to 30W of power. Unlike usb, most ethernet devices have some kind of security built in (firewalls, access control,) and its a data line too so you can do all the smart home/smart energy stuff you want to. > > I think its a great idea, but no demand for it. Personally, im much more interested in [contact and wireless charging like the palm pre does](http://www.engadget.com/2009/01/08/palm-pres-wireless-charger/). Id love a long pad of this stuff on my kitchen counter where I can toss my phone, laptop, camera,mp3 player, etc and have them negotiate a proper level of power and charge without me messing with cables ever again. Toss in wifi and they can do data while charging. I could see myself spending a little coin for that. DC outlets? Not so much. USB everywhere? No thanks. These are yesterday’s problems and yesterday’s technologies. POE works well for low power devices and, as you say, has not become widespread. Some people misoverestimate what people will do to get rid of a wallwart or a cable. IrDA are two technologies designed to get rid of computer cable clutter and they both had zero success in this. WIFi has had more success but the focus is totally different. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 3, 2009, 2:41am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/93 "2009-07-03T02:41:46Z")
> [@sailor](#): > > IrDA are two technologies designed to get rid of computer cable clutter and they both had zero success in this. Should be “IrDA and Bluetooth are two technologies…” ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [July 3, 2009, 3:13am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/94 "2009-07-03T03:13:45Z")
as was mentioned earlier the way to go for this is a small solar/wind setup, then wire it to low voltage 12 volt LEDs and to cigarette lighter sockets and USB. You can wire up a system like this very easily, I have such a setup that I use for providing basic lighting and power for market stalls at festivals. the REUK website has a lot of info about wiring up low voltage circuits and neat tricks like making a wind turbine using the stepper motors from old broken printers. [http://www.reuk.co.uk/Shed-and-Garage-Solar-Lighting.htm](http://www.reuk.co.uk/Shed-and-Garage-Solar-Lighting.htm) [http://www.reuk.co.uk/Electricity-with-Stepper-Motors.htm](http://www.reuk.co.uk/Electricity-with-Stepper-Motors.htm) There are also some houses around where I live now (northern rivers Australia) which have no mains connections and are on Solar power only with battery banks and as well as having 240 volts from invertors they are wired to provide direct 12 volt DC power, usually though cigarette lighter sockets. ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [July 3, 2009, 4:59am UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/95 "2009-07-03T04:59:51Z")
\>You made an excellent point regarding USB, but I’m not sure what you’re arguing now… My point is that 100mw is next to nothing. If we’re going to shove a solution down people’s throats then it should be 100W minimum, not 100mw. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 4:59pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/96 "2009-07-03T16:59:10Z")
> [@HorseloverFat](#): > > \>You made an excellent point regarding USB, but I’m not sure what you’re arguing now… > > My point is that 100mw is next to nothing. If we’re going to shove a solution down people’s throats then it should be 100W minimum, not 100mw. I wasn’t PROPOSING to make 2W USB the standard! God, for every one constructive, sensible criticism/suggestion, there is five totally off-the-wall, retarded points. > [@sailor](#): > > Same current, same wire, same voltage drop: 1/10th the power, 10 times the voltage drop as regards voltage. 6V drop in 120 V is 5% and acceptable. 6V drop in 12 is no longer 12 V. And this for 1/10th the power which can be transmitted using 120 V. And 50% lost in the wire. I do not think you have thought this through have you? Touche about the voltage drop as an absolute value. I’d forgotten about that. However, wires don’t get chosen by their voltage drop, per se, under normal circumstances, but by the heat they output, (the heat they output under foreseeable overload conditions), and how that heat could be bottled up over hours or days, raising the resistance further, and causing a conceivable safety hazard. To put some numbers to it, the common house wire is #14 (1.6mm diameter). When made of copper, it has a resistance of 8 ohm/km. To get a 6V drop, as you wave about, would take a current of 48A over a distance of one kilometer, or 16A (200W) over two miles. Is your house two miles in radius? No? Next time, try putting numbers to things yourself. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 5:07pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/97 "2009-07-03T17:07:57Z")
PoE is another good standard, capable of 30W and auto-voltage negotiation. Homes need ethernet anyway, after all, and many of my wallwarts go straight to networking gear. The worst thing about PoE is that the ethernet connector is fairly fragile, large, and inconvenient (although, its huge advantage is ease to splice by hand). PoE is a very cool tech with a very clear path to ubiquity. Whoever wanted to do a long bet against home DC, would you admit defeat if every new home started to feature pre-wired Ethernet with PoE? ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 5:11pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/98 "2009-07-03T17:11:17Z")
> [@HorseloverFat](#): > > Personally, im much more interested in [contact and wireless charging like the palm pre does](http://www.engadget.com/2009/01/08/palm-pres-wireless-charger/). Id love a long pad of this stuff on my kitchen counter where I can toss my phone, laptop, camera,mp3 player, etc and have them negotiate a proper level of power and charge without me messing with cables ever again. Toss in wifi and they can do data while charging. I could see myself spending a little coin for that. DC outlets? Not so much. USB everywhere? No thanks. These are yesterday’s problems and yesterday’s technologies. Wireless power is obviously a tech that intrigues many people, but if you were bitching about the lower power that USB puts out, you won’t be happy with this either. And would you like a wallwart with your kitchen counter, too? ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 3, 2009, 5:18pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/99 "2009-07-03T17:18:44Z")
> [@Alex\_Dubinsky](#): > > To put some numbers to it, the common house wire is #14 (1.6mm diameter). When made of copper, it has a resistance of 8 ohm/km. To get a 6V drop, as you wave about, would take a current of 48A over a distance of one kilometer, or 16A (200W) over two miles. My apologies! That should be 0.75A over one kilometer, or 16A over 150 feet. That’s a quite a bit different, but still shows that you won’t be getting a 6V drop for most homes (when trying to run 200W). A standard that uses 48V or one that only lets lower-power electronics to connect would work better. ---
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [July 3, 2009, 5:25pm UTC](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891/100 "2009-07-03T17:25:59Z")
> [@Alex\_Dubinsky](#): > > However, wires don’t get chosen by their voltage drop, per se, under normal circumstances, but by the heat they output, (the heat they output under foreseeable overload conditions), and how that heat could be bottled up over hours or days, raising the resistance further, and causing a conceivable safety hazard. I’m not sure about the NEC but the Canadian Electrical Code (which is very similar) mandates a maximum voltage drop of 5% from the supply side to the point of utilization and not more than 3% on any branch circuit. > [@Alex\_Dubinsky](#): > > To put some numbers to it, the common house wire is #14 (1.6mm diameter). When made of copper, it has a resistance of… These numbers aren’t to refute or support yours, I just figured since I had my code book out I’d run them through: #14 AWG wire is permitted to carry 15A max on a resistive load so most tables don’t go that high for 14 gauge. At 10 amps you’re allowed (in Canada) to run the circuit 18.3m to stay within the 3% drop on a branch circuit. To get a 6% drop at 10A you would be limited to 135 ft. (per the NEC calculator). [Previous page](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891.md?page=4) [Next page](https://boards.straightdope.com/t/why-the-sam-hill-dont-i-have-dc-in-my-house/500891.md?page=6)